I. Field of the Invention
The present invention relates to circuitry for advancing signal transmission between transmitting and receiving circuits. More specifically, the present invention relates to the implementation of a circuit for coupling transitional energy from a transmitting circuit to a receiving circuit in advance of the normal connective path which contains inherent circuit delay as embodied in a programmable logic driver circuit which further includes overcurrent protection circuitry.
II. Description of the Related Art
In conventional electronic circuits, the output of a transmitting circuit is typically coupled to the input of a receiving circuit. The normal connective path between the output of the transmitting circuit and the input of the receiving circuit typically includes an inherent circuit delay. In many cases, this circuit delay in the normal connective path does not result in optimization in overall performance in a design implementing the transmitting and receiving circuits.
Automatic test equipment (ATE) systems are currently used in the testing of electronic assemblies and subassemblies at various stages in the manufacturing process. For the testing of digital electronic equipment, the ATE system usually incorporates a logic driver for providing logic states to the unit under test. Logic drivers typically may be characterized as including a transmitting circuit responsive to input and control signals with the processed control signals transmitted to a receiving circuit via a connective path. The processed signals are coupled by the normal connective path, which includes inherent circuit delays. The receiving circuit is responsive to the processed control signals for providing an output response in the form of logic signals that are compatible with the unit under test. The ATE system in exercising the unit under test provides predetermined logic states as an input to the test unit. The ATE system then monitors the responses of the unit under test to the predetermined inputs. The response data is used in determining whether the unit under test contains a component or manufacturing related defect.
Logic drivers previously used in ATE systems have been linear-type drivers which utilize linear feedback overcurrent protection circuits if the logic driver circuit included overcurrent protection. When an electrical short occurs at the output of these types of logic driver, due to a defect in the unit under test, the driver momentarily provides a high current output until the overcurrent condition is detected by the driver's overcurrent protection circuit. Once the overcurrent condition is detected, the overcurrent protection circuit regulates the driver output current at a constant predetermined maximum value. During the overcurrent condition, the drive output current is typically higher than the maximum operating current of the driver. Therefore, significant power dissipation occurs during the overcurrent condition. Accordingly, the driver output elements must be capable of handling, on a continuous basis, higher power outputs. As a result, larger capacity heat sinks must be used for the output elements.
In a logic driver providing test signals to a unit under test, in certain cases it is important to provide in the test signals certain rise and fall time and propagation delays to adequately exercise the unit under test. In order to achieve maximum testing capability, the logic driver needs to be faster than the unit under test. The incorporation of a feed forward compensation circuit into the logic driver permits programmable signal propagation.
It is, therefore, an object of the present invention to provide novel and improved circuitry for selectively enabling the coupling of a signal output from a transmitting circuit to a receiving circuit in advance of a normal connective path.
It is yet another object of the present invention to provide a novel and improved programmable high-speed logic driver with overcurrent protection incorporating feed forward compensation.